1. Technical Field
The present disclosure relates to an optical plate and a backlight module using the optical plate.
2. Description of the Related Art
Referring to FIG. 8, a typical direct type backlight module 100 includes a frame 11, a plurality of lamps 12 positioned above a base of the frame 11, a light diffusion plate 13, and a prism sheet 10 stacked on top of the frame 11 in that order. Inside walls of the frame 11 are configured for reflecting certain of the light upwards. The light diffusion plate 13 includes a plurality of dispersion particles (not shown) for scattering light to enhance the uniformity of light exiting the light diffusion plate 13.
Referring to FIG. 9, the prism sheet 10 includes a base layer 101 and a prism layer 103 formed on the base layer 101. The prism layer 103 includes a plurality of parallel prism lenses 105 having a triangular cross section. The prism lenses 105 collimate received light. Typically, a method of manufacturing the prism sheet 10 includes coating the base layer 101 with a melted ultraviolet(UV)-cured transparent resin to form V-shaped lenses, then solidifying the melted UV-cured transparent resin to form the prism lenses 105.
In use, light from the lamps 12 enters the diffusion plate 13 and becomes scattered, before leaving the light diffusion plate 13 to the prism sheet 10. The scattered light then travels through the prism sheet 10 and is refracted out at the prism layer 103 of the prism lenses 105. Thus, the refracted light leaving the prism sheet 10 is concentrated at the prism layer 103 and a brightness (illumination) of the prism sheet 10 is increased. The refracted light then propagates into an LCD panel (not shown) positioned above the prism sheet 10.
However, although light from the light sources 12 enters the diffusion plate 13 and becomes scattered, strong light spots of the light sources 12 directly above the light sources 12 are often formed. Therefore, an upper diffusion film 14 may be positioned on the prism sheet 10 to reduce or eliminate light spots of the light sources 12. Although the upper light diffusion film 14 and the prism sheet 10 are in contact with each other, a plurality of air pockets may still exist around the boundaries of the light diffusion film 14 and the prism sheet 10. When the backlight module 100 is in use, light passes through the air pockets, and some of the light undergoes total reflection by the air pockets along one or more corresponding boundaries. In addition, the upper light diffusion film 14 may absorb a certain amount of the light from the prism sheet 10. As a result, a brightness of light illumination of the backlight module 100 is reduced.
What is needed, therefore, is a new optical plate and a backlight module using the optical plate that can overcome the above-mentioned shortcomings.